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Baby whales ‘thrown over the reef’ during migration due to warmer oceans

Thursday 17 August 2023 | Written by RNZ | Published in Environment, Features, National, Weekend

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Baby whales ‘thrown over the reef’ during migration due to warmer oceans
A dead humpback calf washed ashore at the Mangaia harbour last week. CLIMATE CHANGE COOK ISLANDS/23081610

A whale scientist in the Cook Islands expects beached calves to become a more common occurrence as storms grow in intensity due to climate change. Caleb Fotheringham of RNZ Pacific reports.

It follows a dead humpback calf washing up in the Southern Group island of Mangaia late last week.

“Residents of Mangaia woke up to an unusual sight yesterday morning after a dead baby whale washed ashore at the harbour,” Cook Islands News reported last Saturday.

The island's mayor Anthony Whyte told the newspaper the dead calf, about three metres in length, had “cut marks on it...but there was no evidence of the baby whale being attacked, so we couldn't really determine the cause of death”.

Biologist Nan Hauser, who has spent the past three decades studying humpback whales, told RNZ Pacific that beached calves “is becoming scary”, as humpback whales migrate to the Pacific Islands from Southern feeding grounds to mate and give birth.

“Because of climate change, we're getting so much intense weather, currents are changing, waves are getting higher, and storms are getting more intense,” she said.

“We're actually seeing these calves being pushed away from their mothers and thrown over the reef, and then they're separated.”

Last August, a humpback calf had come over the reef in Aitutaki.

“When we saw that happening last year, I remember speaking to people around the world about it and they were also worrying that we would see more of that,” Hauser said.

She said whale migration patterns “has to change” but there is little understanding on how it actually works.

“It's almost as if the migratory pathways and the corridors and the whole migration pattern is hardwired, it's like ancestral knowledge, its memory, into their DNA.

“And so, all of a sudden, they have to change all this, because where they're going the water's too warm and their food's not there anymore.”

With climate change causing the ocean to become warmer, she said that “also tricks the biological clock of these animals into thinking…it's time to migrate”.

“Maybe they're not as fat as they should be, maybe they don't have as much blubber because they don't eat after they leave Antarctica for sometimes six to eight months. They fast.

“They have to carry all that water in their bodies in their blubber to produce milk and if the mother's not all that healthy, then the calves are not going to have the proper nutrition itself.”

Hauser said since she began her research in 1998, humpback whales would start showing up on Rarotonga around June, with the migratory season starting and by July, the season would be fully active.

However, she said now the whales do not show up until August.

“We have whales that show up and pass through because we're just a corridor; they come through here on their way to true breeding grounds, like Niue or Tonga or New Caledonia.

“But when they show up later here, they don't spend as much time here either. Since I've been here since 1998 It's been delayed by six or seven weeks over the past couple of decades.”